[InstCombine] Retain TBAA when narrowing memory accesses

Summary:
As discussed on the mailing list it is legal to propagate TBAA to loads/stores
from/to smaller regions of a larger load tagged with TBAA. Do so for
(load->extractvalue)=>(gep->load) and similar foldings.

Reviewed By: sanjoy
Differential Revision: https://reviews.llvm.org/D31954

llvm-svn: 306615

2 files changed, 29 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index ca370c73fca..26bee204e5a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -661,6 +661,9 @@ static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
     if (NumElements == 1) {
       LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
                                                ".unpack");
+      AAMDNodes AAMD;
+      LI.getAAMetadata(AAMD);
+      NewLoad->setAAMetadata(AAMD);
       return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
         UndefValue::get(T), NewLoad, 0, Name));
     }
@@ -690,6 +693,10 @@ static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
                                                 Name + ".elt");
       auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
       auto *L = IC.Builder->CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
+      // Propagate AA metadata. It'll still be valid on the narrowed load.
+      AAMDNodes AAMD;
+      LI.getAAMetadata(AAMD);
+      L->setAAMetadata(AAMD);
       V = IC.Builder->CreateInsertValue(V, L, i);
     }
 
@@ -702,6 +709,9 @@ static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
     auto NumElements = AT->getNumElements();
     if (NumElements == 1) {
       LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
+      AAMDNodes AAMD;
+      LI.getAAMetadata(AAMD);
+      NewLoad->setAAMetadata(AAMD);
       return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
         UndefValue::get(T), NewLoad, 0, Name));
     }
@@ -734,6 +744,9 @@ static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
                                                 Name + ".elt");
       auto *L = IC.Builder->CreateAlignedLoad(Ptr, MinAlign(Align, Offset),
                                               Name + ".unpack");
+      AAMDNodes AAMD;
+      LI.getAAMetadata(AAMD);
+      L->setAAMetadata(AAMD);
       V = IC.Builder->CreateInsertValue(V, L, i);
       Offset += EltSize;
     }
@@ -1192,7 +1205,11 @@ static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
                                                 AddrName);
       auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
       auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
-      IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
+      llvm::Instruction *NS =
+          IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
+      AAMDNodes AAMD;
+      SI.getAAMetadata(AAMD);
+      NS->setAAMetadata(AAMD);
     }
 
     return true;
@@ -1239,7 +1256,10 @@ static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
                                                 AddrName);
       auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
       auto EltAlign = MinAlign(Align, Offset);
-      IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
+      Instruction *NS = IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
+      AAMDNodes AAMD;
+      SI.getAAMetadata(AAMD);
+      NS->setAAMetadata(AAMD);
       Offset += EltSize;
     }
 
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 02fac4fb37a..723414635d6 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2425,9 +2425,15 @@ Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
       Builder->SetInsertPoint(L);
       Value *GEP = Builder->CreateInBoundsGEP(L->getType(),
                                               L->getPointerOperand(), Indices);
+      Instruction *NL = Builder->CreateLoad(GEP);
+      // Whatever aliasing information we had for the orignal load must also
+      // hold for the smaller load, so propagate the annotations.
+      AAMDNodes Nodes;
+      L->getAAMetadata(Nodes);
+      NL->setAAMetadata(Nodes);
       // Returning the load directly will cause the main loop to insert it in
       // the wrong spot, so use replaceInstUsesWith().
-      return replaceInstUsesWith(EV, Builder->CreateLoad(GEP));
+      return replaceInstUsesWith(EV, NL);
     }
   // We could simplify extracts from other values. Note that nested extracts may
   // already be simplified implicitly by the above: extract (extract (insert) )